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The OpenCV (Open Source Computer Vision) library provided the implementations for many of the methods explained in this module. Detailed explanations of the functionality are available on the OpenCV website.

Why use color isolation?

Many computer vision methods exist for feature detection (such as detecting faces or characters in an image). We wanted the possibility to track multiple types of objects with our virtual theremin. Feature detection does not allow for this flexibility. We also needed our object recognition to be fast in order to drive real time audio. Feature detection algorithms work, but are known to be a bit slow. In order to address these concerns, we opted to use color to track objects. When the user launches our program, the user must select the object they wish to track. The color of this object is stored by the program. Every future frame retrieved by the webcam is scanned for all pixels within range of that color, allowing for the isolation of the object after a few steps.

Color spaces


Cameras operate in the RGB color space. In the RGB color space, images store three channels of information: red, green, and blue. For each channel, 8 bits of data is stored. RGB images use additive color mixing: zeros in all channels represents black and 255 in each channel represents white. Although this color space is easy to use, highlight and shadow affect RGB values. Therefore, tracking using RGB values is not a realistic option to track a constant color.


Our virtual theremin first converts RGB to HSV. HSV is an alternative color space that uses three different channels of information: Hue, Saturation, and Value. The HSV color space represents colors according to the figure below. Unlike RGB, highlight and shadow do not cause changes in hue values. Therefore, it is possible to track an object in variable lighting conditions using HSV. The conversion to HSV from RGB is as follows:

HSV Equations HSV Equations HSV Equations
HSV Color Space
The HSV Color Space

If the above formula results in H less than 0, it is converted to H+360.

Object detection

Gaussian blur

Before any detection is attempted, a slight blur is applied to the image using a Gaussian kernel. This blur smoothes out any noise in the initial image. The blurred image is then converted to the HSV color space.

Original Image
Original Image
HSV Image
HSV Image
Original and HSV Images

Image thresholding

The user initially selects a point in the image. The HSV value at this point is used as the center color in the threshold range. Using the values set by the margin sliders, the HSV image is converted to a binary image by thresholding the HSV image to the specified range around the selected color.

Thresholded Image
Thresholded Image

Object isolation

Depending on the environment, the thresholding image may or may not contain other noise. The example photo was taken against a solid background of a different color. Therefore, there is no other noise visible in this image. However, in order to determine which portion of the thresholded image is our desired object, we assume that noise is present.

We first find all of the contours from the edges in the thresholded image. For each found contour, we compute the area enclosed. We assume that the contour enclosing the largest area is the desired object. Once this specific contour has been determined, we fit an ellipse to the contour. From this ellipse, we can determine the angle of the major axis and the position of the center. The isolated image, shown below, has this ellipse drawn in red around the contour shaded in blue.

Isolated Image
Isolated Image

Questions & Answers

what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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Source:  OpenStax, Virtual theremin. OpenStax CNX. Dec 18, 2013 Download for free at http://cnx.org/content/col11605/1.1
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